A characteristic of microwave cooking is that the exterior of foods cooked in a microwave oven, such as breads, do not have a brown or crisp texture desired by consumers. An objective of those concerned with microwave cooking has therefore been to provide ways of browning or crisping the exterior of foods cooked in a microwave oven.
One technique developed to brown or crisp the exterior of foods during microwave cooking has been the incorporation of a microwave interactive laminate into packages which contain foods. In response to microwave energy, a microwave interactive layer of the laminate generates heat which browns or crisps the surface of food.
Typically, a microwave interactive laminate includes a thin film which has a microwave interactive layer of lossy material deposited onto one side of the film. The layer of material generates heat in response to microwave energy. Film with a microwave interactive layer deposited on one side is a microwave interactive film.
To form a microwave interactive laminate, the microwave interactive film is bonded to a substrate, which substrate serves as a support structure. The microwave interactive layer is between the film and the substrate. The laminate may subsequently be cut into a shape that approximates the shape of a particular food product or the size of a particular package.
Commercially, microwave interactive laminate can most conveniently be cut into rectangles for use in packages. When the food product which is being heated is circular, triangular or some other shape which does not conform to a rectangle, heat-generating areas of the microwave interactive laminate will not be covered by the food product. The exposed areas of conventional microwave interactive laminate can produce excessive heat which can scorch the food or the container. Also, the efficiency of the microwave interactive laminate is diminished when heat-generating areas are not covered by the food product since the exposed heat-generating areas absorb microwave radiation that would otherwise brown or crisp the food.
In addition, the heat-generating areas of a microwave interactive laminate can overlap each other when a package is assembled. Excessive heat is generated at the areas of overlap which can scorch the food or the package.
Finally, in packages where the microwave interactive laminate covers only a portion of a package or container, adhesive used to bond the microwave interactive laminate to the package or container can extend outside the area covered by the microwave interactive laminate. Adhesive outside the area of a package surface covered by the microwave interactive laminate can cause packages to stick together during production and handling.
Microwave interactive laminates formed in accordance with the present invention have a microwave interactive layer with a heating area or areas of any desired shape. Excessive heat generation caused by exposed or overlapping microwave interactive laminates can thus be avoided by the present invention.